2,339 research outputs found
Transmit design for MIMO wiretap channel with a malicious jammer
In this paper, we consider the transmit design for multi-input multi-output
(MIMO) wiretap channel including a malicious jammer. We first transform the
system model into the traditional three-node wiretap channel by whitening the
interference at the legitimate user. Additionally, the eavesdropper channel
state information (ECSI) may be fully or statistically known, even unknown to
the transmitter. Hence, some strategies are proposed in terms of different
levels of ECSI available to the transmitter in our paper. For the case of
unknown ECSI, a target rate for the legitimate user is first specified. And
then an inverse water-filling algorithm is put forward to find the optimal
power allocation for each information symbol, with a stepwise search being used
to adjust the spatial dimension allocated to artificial noise (AN) such that
the target rate is achievable. As for the case of statistical ECSI, several
simulated channels are randomly generated according to the distribution of
ECSI. We show that the ergodic secrecy capacity can be approximated as the
average secrecy capacity of these simulated channels. Through maximizing this
average secrecy capacity, we can obtain a feasible power and spatial dimension
allocation scheme by using one dimension search. Finally, numerical results
reveal the effectiveness and computational efficiency of our algorithms.Comment: 2015 IEEE 81st Vehicular Technology Conference (VTC Spring
Simulating Z_2 topological insulators with cold atoms in a one-dimensional optical lattice
We propose an experimental scheme to simulate and detect the properties of
time-reversal invariant topological insulators, using cold atoms trapped in
one-dimensional bichromatic optical lattices. This system is described by a
one-dimensional Aubry-Andre model with an additional SU(2) gauge structure,
which captures the essential properties of a two-dimensional Z2 topological
insulator. We demonstrate that topologically protected edge states, with
opposite spin orientations, can be pumped across the lattice by sweeping a
laser phase adiabatically. This process constitutes an elegant way to transfer
topologically protected quantum states in a highly controllable environment. We
discuss how density measurements could provide clear signatures of the
topological phases emanating from our one-dimensional system.Comment: 5 pages +, 3 figures, to appear in Physical Review
Scalable quantum information processing with atomic ensembles and flying photons
We present a scheme for scalable quantum information processing (QIP) with
atomic ensembles and flying photons. Using the Rydberg blockade, we encode the
qubits in the collective atomic states, which could be manipulated fast and
easily due to the enhanced interaction, in comparison to the single-atom case.
We demonstrate that our proposed gating could be applied to generation of
two-dimensional cluster states for measurement-based quantum computation.
Moreover, the atomic ensembles also function as quantum repeaters useful for
long distance quantum state transfer. We show the possibility of our scheme to
work in bad cavity or in weak coupling regime, which could much relax the
experimental requirement. The efficient coherent operations on the ensemble
qubits enable our scheme to be switchable between quantum computation and
quantum communication using atomic ensembles.Comment: 8 pages, 7 figure
Probing Half-odd Topological Number with Cold Atoms in a Non-Abelian Optical Lattice
We propose an experimental scheme to probe the contribution of a single Dirac
cone to the Hall conductivity as half-odd topological number sequence. In our
scheme, the quantum anomalous Hall effect as in graphene is simulated with cold
atoms trapped in an optical lattice and subjected to a laser-induced
non-Abelian gauge field. By tuning the laser intensity to change the gauge
flux, the energies of the four Dirac points in the first Brillouin zone are
shifted with each other and the contribution of the single Dirac cone to the
total atomic Hall conductivity is manifested. We also show such manifestation
can be experimentally probed with atomic density profile measurements.Comment: 5 pages, 3 figure
Bioactivity of Cicuta virosa L. var. latisecta Celak. (Umbelliferae: Cicutal) against Red Imported Fire Ant under Laboratory and Field Conditions
We evaluated the bioactivities of compounds from Cicuta virosa L. var. latisecta Celak. against red imported fire ants (Solenopsis invicta Buren) under field and laboratory conditions. The compounds were as follows: methanol extract; petroleum ether, chloroform, and ethyl acetate fractions from the methanol extract; and the active compound isoimperatorin, which was isolated from the chloroform-fraction. The 7 d LC50 values of the methanol extract, petroleum ether, chloroform, and ethyl acetate fractions and isoimperatorin toward micrergates were 111.20, 214.45, 40.90, 569.67, and 25.73 mg/kg, respectively. The corresponding LC50 values toward macrergates were 155.78, 308.38, 75.01, 776.75, and 42.77 mg/kg, respectively. Under field conditions, baits containing 0.2% methanol extract, 0.1% chloroform fraction, and 0.05% isoimperatorin efficiently controlled S. invicta, with effectiveness percentages of 95.56%, 97.78%, and 95.56%, respectively on the 30th day after bait application. Such effectiveness percentages were not significantly different from that obtained using the positive control fipronil. The present study showed that C. virosa L. var. latisecta has potential as a natural control agent for the red imported fire ants
Toxicological evaluation of precocene II isolated from Ageratum conyzoides L. (Asteraceae) in Sprague Dawley rats
Precocene II (6,7-dimethoxy-2,2-dimethyl-2-chromene) was the main constituent isolated from Ageratum
conyzoides L. and reportedly possessed antifungal activity. The study investigated the isolation,
purification and toxicological effects of precocene II from A. conyzoides in Sprague Dawley rats.
Precocene II was isolated from the petroleum ether fraction of the plant and the structure was
determined by 1H-,13C-,DEPT-NMR and MS spectral techniques. Three groups of eight rats per group
were used for the study. While groups B and C were respectively administered with 25 and 50 mg/kg of
precocene II in 0.25% CMC-Na for 11 days by gastric intubation, group A was administered with 0.25%
CMC-Na and served as the control group. After the last treatment, animals were fasted overnight and on
the 12th day, they were injected intravenously with 0.2 ml/kg body weight of phenobarbital. Animals
were subsequently dissected from the abdominal region; blood was collected from the pulmonary vein
into EDTA anti-coagulated and non anti-coagulated tubes. The liver, kidney and spleen tissues were
extracted into separate bottles for histopathological examinations. Results from hematological study
indicated that the white blood cell (WBC), red blood cell (RBC), plateletcrit (PCT) and mean corpuscular hemoglobin count (MCHC) were significantly higher across the treated groups. Biochemical result showed that serum glucose level was significantly reduced in the treated groups. No apparent damage was noticed in the liver, kidney and spleen tissues. The result therefore suggests that precocene II
possesses hypoglycemic property and could alter some hematopoietic elements but was not toxic to the liver, kidney and spleen tissues
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